Normal operation of integrated circuits requires less and less operating voltage as technology continues to improve. As operating voltages for integrated circuits continue to shrink, voltage differences previously relied upon to be available for operating integrated circuits are becoming strained. Where once an operating supply voltage Vcc was on the order of 5 volts, supply voltages have dropped into the range of 1.2 volts. Supply voltages at this level are close to the threshold voltages of the devices that are being operated in a circuit.
When systems with low supply voltages are operated, current capabilities of devices are sometimes reduced due to the lack of sufficient voltage to fully turn on or turn off transistors and the like. When this happens, unreliable operation of the devices, and therefore the circuits, can create numerous issues, including failure of the part to perform as desired and the like. In memory devices, such an improper operation can result in lost data or incorrectly written data.
In order to provide sufficient operating voltages when supply voltages continue to drop, level shifters are used. Typical level shifter circuitry operates on a fairly narrow range of supply voltages. A previous level shifter 100 is shown in FIG. 1. Level shifter 100 comprises cross coupled p-channel metal oxide semiconductor (PMOS) transistors 102 and 104, and NMOS transistors 106 and 108 gate coupled to complementary inputs. Output is taken at node 110 and complementary output node 112.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved low level voltage shifting.